[PATCH v5 07/12] drm/ttm: Use the LRU walker for eviction
Matthew Brost
matthew.brost at intel.com
Wed Jun 19 23:33:31 UTC 2024
On Tue, Jun 18, 2024 at 09:18:15AM +0200, Thomas Hellström wrote:
> Use the LRU walker for eviction. This helps
> removing a lot of code with weird locking
> semantics.
>
> The functionality is slightly changed so that
> when trylocked buffer objects are exhausted, we
> continue to interleave walks with ticket-locks while
> there is still progress made. The list walks are
> not restarted in-between evictions.
>
> Also provide a separate ttm_bo_evict_first()
> function for its single user. The context of that
> user allows sleeping dma_resv locks.
>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Somalapuram Amaranath <Amaranath.Somalapuram at amd.com>
> Cc: Matthew Brost <matthew.brost at intel.com>
> Cc: <dri-devel at lists.freedesktop.org>
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> ---
> drivers/gpu/drm/ttm/ttm_bo.c | 350 ++++++++++++-----------------
> drivers/gpu/drm/ttm/ttm_resource.c | 20 +-
> include/drm/ttm/ttm_bo.h | 8 +-
> 3 files changed, 145 insertions(+), 233 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index 63a91b77f7da..316afe19a325 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -224,80 +224,6 @@ static void ttm_bo_flush_all_fences(struct ttm_buffer_object *bo)
> dma_resv_iter_end(&cursor);
> }
>
> -/**
> - * ttm_bo_cleanup_refs
> - * If bo idle, remove from lru lists, and unref.
> - * If not idle, block if possible.
> - *
> - * Must be called with lru_lock and reservation held, this function
> - * will drop the lru lock and optionally the reservation lock before returning.
> - *
> - * @bo: The buffer object to clean-up
> - * @interruptible: Any sleeps should occur interruptibly.
> - * @no_wait_gpu: Never wait for gpu. Return -EBUSY instead.
> - * @unlock_resv: Unlock the reservation lock as well.
> - */
> -
> -static int ttm_bo_cleanup_refs(struct ttm_buffer_object *bo,
> - bool interruptible, bool no_wait_gpu,
> - bool unlock_resv)
> -{
> - struct dma_resv *resv = &bo->base._resv;
> - int ret;
> -
> - if (dma_resv_test_signaled(resv, DMA_RESV_USAGE_BOOKKEEP))
> - ret = 0;
> - else
> - ret = -EBUSY;
> -
> - if (ret && !no_wait_gpu) {
> - long lret;
> -
> - if (unlock_resv)
> - dma_resv_unlock(bo->base.resv);
> - spin_unlock(&bo->bdev->lru_lock);
> -
> - lret = dma_resv_wait_timeout(resv, DMA_RESV_USAGE_BOOKKEEP,
> - interruptible,
> - 30 * HZ);
> -
> - if (lret < 0)
> - return lret;
> - else if (lret == 0)
> - return -EBUSY;
> -
> - spin_lock(&bo->bdev->lru_lock);
> - if (unlock_resv && !dma_resv_trylock(bo->base.resv)) {
> - /*
> - * We raced, and lost, someone else holds the reservation now,
> - * and is probably busy in ttm_bo_cleanup_memtype_use.
> - *
> - * Even if it's not the case, because we finished waiting any
> - * delayed destruction would succeed, so just return success
> - * here.
> - */
> - spin_unlock(&bo->bdev->lru_lock);
> - return 0;
> - }
> - ret = 0;
> - }
> -
> - if (ret) {
> - if (unlock_resv)
> - dma_resv_unlock(bo->base.resv);
> - spin_unlock(&bo->bdev->lru_lock);
> - return ret;
> - }
> -
> - spin_unlock(&bo->bdev->lru_lock);
> - ttm_bo_cleanup_memtype_use(bo);
> -
> - if (unlock_resv)
> - dma_resv_unlock(bo->base.resv);
> -
> - return 0;
> -}
> -
> /*
> * Block for the dma_resv object to become idle, lock the buffer and clean up
> * the resource and tt object.
> @@ -505,151 +431,154 @@ bool ttm_bo_eviction_valuable(struct ttm_buffer_object *bo,
> }
> EXPORT_SYMBOL(ttm_bo_eviction_valuable);
>
> -/*
> - * Check the target bo is allowable to be evicted or swapout, including cases:
> - *
> - * a. if share same reservation object with ctx->resv, have assumption
> - * reservation objects should already be locked, so not lock again and
> - * return true directly when either the opreation allow_reserved_eviction
> - * or the target bo already is in delayed free list;
> +/**
> + * ttm_bo_evict_first() - Evict the first bo on the manager's LRU list.
> + * @bdev: The ttm device.
> + * @man: The manager whose bo to evict.
> + * @ctx: The TTM operation ctx governing the eviction.
> *
> - * b. Otherwise, trylock it.
> + * Return: 0 if successful or the resource disappeared. Negative error code on error.
> */
> -static bool ttm_bo_evict_swapout_allowable(struct ttm_buffer_object *bo,
> - struct ttm_operation_ctx *ctx,
> - const struct ttm_place *place,
> - bool *locked, bool *busy)
> +int ttm_bo_evict_first(struct ttm_device *bdev, struct ttm_resource_manager *man,
> + struct ttm_operation_ctx *ctx)
> {
> - bool ret = false;
> + struct ttm_resource_cursor cursor;
> + struct ttm_buffer_object *bo;
> + struct ttm_resource *res;
> + unsigned int mem_type;
> + int ret = 0;
>
> - if (bo->pin_count) {
> - *locked = false;
> - if (busy)
> - *busy = false;
> - return false;
> + spin_lock(&bdev->lru_lock);
> + res = ttm_resource_manager_first(man, &cursor);
> + if (!res) {
> + ret = -ENOENT;
> + goto out_no_ref;
> }
> + bo = res->bo;
> + if (!ttm_bo_get_unless_zero(bo))
> + goto out_no_ref;
> + mem_type = res->mem_type;
> + spin_unlock(&bdev->lru_lock);
> + ret = ttm_bo_reserve(bo, ctx->interruptible, ctx->no_wait_gpu, NULL);
> + if (ret)
> + goto out_no_lock;
> + if (bo->resource != res || res->mem_type != mem_type)
> + goto out_bad_res;
>
> - if (bo->base.resv == ctx->resv) {
> - dma_resv_assert_held(bo->base.resv);
> - if (ctx->allow_res_evict)
> - ret = true;
> - *locked = false;
> - if (busy)
> - *busy = false;
> + if (bo->deleted) {
> + ret = ttm_bo_wait_ctx(bo, ctx);
> + if (ret)
> + ttm_bo_cleanup_memtype_use(bo);
> } else {
> - ret = dma_resv_trylock(bo->base.resv);
> - *locked = ret;
> - if (busy)
> - *busy = !ret;
> - }
> -
> - if (ret && place && (bo->resource->mem_type != place->mem_type ||
> - !bo->bdev->funcs->eviction_valuable(bo, place))) {
> - ret = false;
> - if (*locked) {
> - dma_resv_unlock(bo->base.resv);
> - *locked = false;
> - }
> + ret = ttm_bo_evict(bo, ctx);
> }
> -
> +out_bad_res:
> + dma_resv_unlock(bo->base.resv);
> +out_no_lock:
> + ttm_bo_put(bo);
> + ttm_resource_cursor_fini(&cursor);
> return ret;
> +
> +out_no_ref:
> + ttm_resource_cursor_fini_locked(&cursor);
> + spin_unlock(&bdev->lru_lock);
> + return -ENOENT;
> }
>
> /**
> - * ttm_mem_evict_wait_busy - wait for a busy BO to become available
> - *
> - * @busy_bo: BO which couldn't be locked with trylock
> - * @ctx: operation context
> - * @ticket: acquire ticket
> - *
> - * Try to lock a busy buffer object to avoid failing eviction.
> + * struct ttm_bo_evict_walk - Parameters for the evict walk.
> */
> -static int ttm_mem_evict_wait_busy(struct ttm_buffer_object *busy_bo,
> - struct ttm_operation_ctx *ctx,
> - struct ww_acquire_ctx *ticket)
> -{
> - int r;
> -
> - if (!busy_bo || !ticket)
> - return -EBUSY;
> -
> - if (ctx->interruptible)
> - r = dma_resv_lock_interruptible(busy_bo->base.resv,
> - ticket);
> - else
> - r = dma_resv_lock(busy_bo->base.resv, ticket);
> -
> - /*
> - * TODO: It would be better to keep the BO locked until allocation is at
> - * least tried one more time, but that would mean a much larger rework
> - * of TTM.
> - */
> - if (!r)
> - dma_resv_unlock(busy_bo->base.resv);
> -
> - return r == -EDEADLK ? -EBUSY : r;
> -}
> +struct ttm_bo_evict_walk {
> + /** @walk: The walk base parameters. */
> + struct ttm_lru_walk walk;
> + /** @place: The place passed to the resource allocation. */
> + const struct ttm_place *place;
> + /** @evictor: The buffer object we're trying to make room for. */
> + struct ttm_buffer_object *evictor;
> + /** @res: The allocated resource if any. */
> + struct ttm_resource **res;
> + /** @evicted: The number of evicted pages. */
> + unsigned long evicted;
> +};
>
> -int ttm_mem_evict_first(struct ttm_device *bdev,
> - struct ttm_resource_manager *man,
> - const struct ttm_place *place,
> - struct ttm_operation_ctx *ctx,
> - struct ww_acquire_ctx *ticket)
> +static long ttm_bo_evict_cb(struct ttm_lru_walk *walk, struct ttm_buffer_object *bo)
> {
> - struct ttm_buffer_object *bo = NULL, *busy_bo = NULL;
> - struct ttm_resource_cursor cursor;
> - struct ttm_resource *res;
> - bool locked = false;
> - int ret;
> + struct ttm_bo_evict_walk *evict_walk =
> + container_of(walk, typeof(*evict_walk), walk);
> + long lret;
>
> - spin_lock(&bdev->lru_lock);
> - ttm_resource_manager_for_each_res(man, &cursor, res) {
> - bool busy;
> -
> - if (!ttm_bo_evict_swapout_allowable(res->bo, ctx, place,
> - &locked, &busy)) {
> - if (busy && !busy_bo && ticket !=
> - dma_resv_locking_ctx(res->bo->base.resv))
> - busy_bo = res->bo;
> - continue;
> - }
> + if (!bo->bdev->funcs->eviction_valuable(bo, evict_walk->place))
> + return 0;
>
> - if (ttm_bo_get_unless_zero(res->bo)) {
> - bo = res->bo;
> - break;
> - }
> - if (locked)
> - dma_resv_unlock(res->bo->base.resv);
> + if (bo->deleted) {
> + lret = ttm_bo_wait_ctx(bo, walk->ctx);
> + if (!lret)
> + ttm_bo_cleanup_memtype_use(bo);
> + } else {
> + lret = ttm_bo_evict(bo, walk->ctx);
> }
> - ttm_resource_cursor_fini_locked(&cursor);
>
> - if (!bo) {
> - if (busy_bo && !ttm_bo_get_unless_zero(busy_bo))
> - busy_bo = NULL;
> - spin_unlock(&bdev->lru_lock);
> - ret = ttm_mem_evict_wait_busy(busy_bo, ctx, ticket);
> - if (busy_bo)
> - ttm_bo_put(busy_bo);
> - return ret;
> - }
> + if (lret)
> + goto out;
>
> - if (bo->deleted) {
> - ret = ttm_bo_cleanup_refs(bo, ctx->interruptible,
> - ctx->no_wait_gpu, locked);
> - ttm_bo_put(bo);
> - return ret;
> - }
> + evict_walk->evicted++;
> + if (evict_walk->res)
> + lret = ttm_resource_alloc(evict_walk->evictor, evict_walk->place,
> + evict_walk->res);
> + if (lret == 0)
> + return 1;
> +out:
> + /* Errors that should terminate the walk. */
> + if (lret == -ENOMEM || lret == -EINTR || lret == -ERESTARTSYS ||
> + lret == -EAGAIN)
> + return lret;
>
> - spin_unlock(&bdev->lru_lock);
> + return 0;
> +}
>
> - ret = ttm_bo_evict(bo, ctx);
> - if (locked)
> - ttm_bo_unreserve(bo);
> - else
> - ttm_bo_move_to_lru_tail_unlocked(bo);
> +static const struct ttm_lru_walk_ops ttm_evict_walk_ops = {
> + .process_bo = ttm_bo_evict_cb,
> +};
>
> - ttm_bo_put(bo);
> - return ret;
> +static int ttm_bo_evict_alloc(struct ttm_device *bdev,
> + struct ttm_resource_manager *man,
> + const struct ttm_place *place,
> + struct ttm_buffer_object *evictor,
> + struct ttm_operation_ctx *ctx,
> + struct ww_acquire_ctx *ticket,
> + struct ttm_resource **res)
> +{
> + struct ttm_bo_evict_walk evict_walk = {
> + .walk = {
> + .ops = &ttm_evict_walk_ops,
> + .ctx = ctx,
> + .ticket = ticket,
> + },
> + .place = place,
> + .evictor = evictor,
> + .res = res,
> + };
> + long lret;
> +
> + evict_walk.walk.trylock_only = true;
> + lret = ttm_lru_walk_for_evict(&evict_walk.walk, bdev, man, 1);
> + if (lret || !ticket)
> + goto out;
> +
> + /* If ticket-locking, repeat while making progress. */
> + evict_walk.walk.trylock_only = false;
> + do {
> + /* The walk may clear the evict_walk.walk.ticket field */
> + evict_walk.walk.ticket = ticket;
> + evict_walk.evicted = 0;
> + lret = ttm_lru_walk_for_evict(&evict_walk.walk, bdev, man, 1);
> + } while (!lret && evict_walk.evicted);
> +out:
> + if (lret < 0)
> + return lret;
> + if (lret == 0)
> + return -EBUSY;
> + return 0;
> }
>
> /**
> @@ -760,6 +689,7 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
> for (i = 0; i < placement->num_placement; ++i) {
> const struct ttm_place *place = &placement->placement[i];
> struct ttm_resource_manager *man;
> + bool may_evict;
>
> man = ttm_manager_type(bdev, place->mem_type);
> if (!man || !ttm_resource_manager_used(man))
> @@ -769,22 +699,21 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
> TTM_PL_FLAG_FALLBACK))
> continue;
>
> - do {
> - ret = ttm_resource_alloc(bo, place, res);
> - if (unlikely(ret && ret != -ENOSPC))
> + may_evict = (force_space && place->mem_type != TTM_PL_SYSTEM);
> + ret = ttm_resource_alloc(bo, place, res);
> + if (ret) {
> + if (ret != -ENOSPC)
> return ret;
> - if (likely(!ret) || !force_space)
> - break;
> -
> - ret = ttm_mem_evict_first(bdev, man, place, ctx,
> - ticket);
> - if (unlikely(ret == -EBUSY))
> - break;
> - if (unlikely(ret))
> + if (!may_evict)
> + continue;
> +
> + ret = ttm_bo_evict_alloc(bdev, man, place, bo, ctx,
> + ticket, res);
> + if (ret == -EBUSY)
> + continue;
> + if (ret)
> return ret;
> - } while (1);
> - if (ret)
> - continue;
> + }
>
> ret = ttm_bo_add_move_fence(bo, man, ctx->no_wait_gpu);
> if (unlikely(ret)) {
> @@ -796,7 +725,6 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
> }
> return 0;
> }
> -
> return -ENOSPC;
> }
>
> diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
> index a03090683e79..6d0c66fc36e3 100644
> --- a/drivers/gpu/drm/ttm/ttm_resource.c
> +++ b/drivers/gpu/drm/ttm/ttm_resource.c
> @@ -508,24 +508,10 @@ int ttm_resource_manager_evict_all(struct ttm_device *bdev,
> };
> struct dma_fence *fence;
> int ret;
> - unsigned i;
> -
> - /*
> - * Can't use standard list traversal since we're unlocking.
> - */
>
> - spin_lock(&bdev->lru_lock);
> - for (i = 0; i < TTM_MAX_BO_PRIORITY; ++i) {
> - while (!list_empty(&man->lru[i])) {
> - spin_unlock(&bdev->lru_lock);
> - ret = ttm_mem_evict_first(bdev, man, NULL, &ctx,
> - NULL);
> - if (ret)
> - return ret;
> - spin_lock(&bdev->lru_lock);
> - }
> - }
> - spin_unlock(&bdev->lru_lock);
> + do {
> + ret = ttm_bo_evict_first(bdev, man, &ctx);
Ooo, just noticed this after my initial review.
This function, ttm_bo_evict_first, will return -ENOENT if
ttm_bo_get_unless_zero returns false breaking this loop. I don't think
that is the correct behavior. If ttm_bo_get_unless_zero returns false on
the head of LRU, that means this is getting destroyed. I don't think in
that what we want do to here. Shouldn't continue the LRU walk evicting
all other BOs on the LRU list?
Matt
> + } while (!ret);
>
> spin_lock(&man->move_lock);
> fence = dma_fence_get(man->move);
> diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
> index 472a55b69afb..148f49f625e4 100644
> --- a/include/drm/ttm/ttm_bo.h
> +++ b/include/drm/ttm/ttm_bo.h
> @@ -415,11 +415,9 @@ long ttm_bo_swapout(struct ttm_device *bdev, struct ttm_operation_ctx *ctx,
> pgoff_t target);
> void ttm_bo_pin(struct ttm_buffer_object *bo);
> void ttm_bo_unpin(struct ttm_buffer_object *bo);
> -int ttm_mem_evict_first(struct ttm_device *bdev,
> - struct ttm_resource_manager *man,
> - const struct ttm_place *place,
> - struct ttm_operation_ctx *ctx,
> - struct ww_acquire_ctx *ticket);
> +int ttm_bo_evict_first(struct ttm_device *bdev,
> + struct ttm_resource_manager *man,
> + struct ttm_operation_ctx *ctx);
> vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
> struct vm_fault *vmf);
> vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> --
> 2.44.0
>
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